Kinetics and mechanism of the reduction of thallium(III) by arsenic(III) in perchloric acid solution

Abstract

Thallium(III) and Arsenic(III) react in aqueous perchloric acid solution to give Tl^I and As^V. The kinetics were followed by determining Tl^IIIiodometrically under critical conditions. The empirical rate law is: –d[Tl^III]//_dd=k₃′[Tl^III][As^III]//_[H⁺](a)k₃′ was found to be 88·5 ± 5·7 min^–1 at 35 ± 0·1 °C. The energy and entropy of activation were found to be 21·5 ± 1 kcal and –15·5 ± 3 cal mol^–1deg^–1 respectively. The reactive species are TlOH²⁺ and HAsO₂. The rate decreases with increasing ionic strength and with decreasing dielectric constant. Chloride ions strongly inhibit the reaction.